Statement regarding federally sponsored research or development

ABSTRACT

A backstop for decelerating and trapping projectiles includes a support structure having an upper surface and at least one bin region shielded from incoming rounds. A projectile trapping medium, preferably a mixture of a resilient granular ballistic medium and a hydrated super absorbent polymer (SAP) gel, is disposed on the upper surface and within the bins. Bins are defined by one or more transverse baffles spanning substantially the entire width of the backstop. The baffles are preferably constructed of a non-ricochet producing material. Natural or induced vibrations will urge trapped rounds downwards into the bins. In embodiments, the lower surface of one or more bins declines toward either or both sides of the backstop, such that vibration urges spent rounds towards collection points along the sides of the backstop. Access ports may be provided in the backstop sidewalls proximate these collection points to allow for removal of spent rounds. The volume removed may be filtered to reclaim projectile trapping medium for reuse in the backstop.

[0001] This Application is a continuation-in-part of application Ser.No. 10/307,427, filed Dec. 2, 2002.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] The invention described herein may be manufactured and used by orfor the United States Government for governmental purposes without thepayment of any royalties thereon.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates generally to the firing ofprojectiles on a range, and, more particularly, to an apparatus andmethod for decelerating and trapping munitions fired on a range.

[0005] 2. Background Description

[0006] In order to maintain proficiency in the use of firearms, it iscommon to engage in target practice on a training range. Traditionally,the primary concern on a training range was the prevention of ricochets.Thus, ranges often use a large dirt berm behind the target to decelerateand trap the bullet.

[0007] More recently, however, considerable concern has been raisedabout the environmental impact of heavy metals (e.g., lead, tungsten,copper) contained within the bullet. Though a bullet fired into a moundof dirt is safely contained from the standpoint of no longer being adangerous projectile, heavy metals within the bullet remain free toleach into the soil, thereby contaminating the environment. Thus,shooting ranges have begun to stress containment and removal of expendedrounds in order to prevent environmental contamination.

[0008] Additionally, there is a growing desire to build shooting rangeswithin enclosed structures. This permits frequent use of the rangeregardless of weather and without excessive travel time. Obviously,however, use of a dirt berm behind the target is impractical for suchindoor ranges.

[0009] Thus, current trends in bullet containment systems focus on twodifferent types of systems. The first, often called a bullet stop andcontainment chamber, has a pair of plates that channel bullets toward anopening in a containment chamber. Inside the containment chamber areimpact plates that slow the bullet to a stop. Unfortunately, suchsystems are relatively expensive and difficult to manufacture andmaintain.

[0010] The second type of containment system is the bullet backstop orbullet trap system. Bullet backstops typically include a back plate madeof steel inclined to the line of fire. On an upper surface of the backplate, a layer of material is disposed to provide a medium fordecelerating and trapping bullets. This layer is several feet thick inthe direction the bullet travels. The impact material is typically aresilient granular material. As a bullet impacts the material, it willdecelerate sufficiently such that, if it does impact the back plate, anyricochet will be minimal.

[0011] A number of bullet traps utilize rubber chunks or chips as theimpact material. For example, U.S. Pat. No. 6,378,870 to Sovine (“the'870 Patent”) teaches the use of relatively large rubber nuggetsdisposed along a plane inclined to the line of fire, while U.S. Pat. No.5,848,794 to Wojcinski et al. (“the '794 Patent”) discloses a similarbullet trap using relatively small rubber granules disposed along aninclined plane. To reduce scatter and sluffing of the impact material,the '794 Patent further teaches the use of a self-healing membranecovering the rubber granules.

[0012] However, trapping systems like those disclosed in the '870 Patentand the '794 Patent lack inherent fire retardant characteristics. Thus,they often suffer from heat and fire problems, especially if the chipsare not treated with a fire retardant, are improperly maintained,contain steel or fiber, or if the chips are relatively small. To combatthese hazards, both the '870 Patent and the '974 Patent teach treatingthe rubber nuggets with a fire retardant. Unfortunately, some fireretardants used in these and other prior art systems tend to wash off,such that traps maintained outdoors may lose their fire retardantcharacteristics during and after a rain if not properly maintained.

[0013] Additionally, though extant systems trap the bullet, theytypically do nothing to stabilize them from an environmental hazardstandpoint. Thus, expended rounds must periodically be recovered fromthe trap to prevent heavy metal leaching and associated environmentalcontamination.

[0014] Nor do prior art systems protect or shield spent rounds fromincoming rounds. As expended rounds accumulate, the possibility ofincoming rounds impacting spent rounds increases, which in turnincreases fire, ricochet, and fragmentation hazards. For example, theentire volume of the bullet trap disclosed in U.S. Pat. No. 6,293,552 toWojcinski et al. (“the '552 Patent”) is exposed to incoming fire. Thisproblem is compounded in traps used with automatic weapons, which arecapable of building up a significant mass of spent bullets in arelatively short period of time, increasing the need to periodically“mine” the trap to reclaim spent rounds.

[0015] To remove accumulated rounds, many prior art systems, such as the'552 Patent and U.S. Pat. No. 6,000,700 to Nesler et al. (“the '700Patent”) teach removal via a trap door or similar access panel. Both the'552 Patent and the '700 Patent utilize a flowable ballistic material,and intend for a combined volume of ballistic material and spent roundsto flow out of the trap during cleaning. Since rounds will impact thetrap at a number of points, however, it is often necessary to remove asubstantial volume of the ballistic material in order to ensure adequatecleaning. Furthermore, the mining process is generally burdensome andtime consuming.

SUMMARY OF THE INVENTION

[0016] Accordingly, it is an object of the present invention to providea bullet trapping system that substantially reduces the likelihood ofricochets, fragmentation, and fire.

[0017] It is another object of the present invention to provide a bullettrapping system that can accommodate many different calibers and typesof bullets delivered by a variety of firearms.

[0018] A further object of the present invention is to provide a bullettrapping system that requires minimal maintenance over an extendeduseful life.

[0019] Still another object of the present invention is to provide abullet trapping system that shields spent rounds from the impact ofincoming rounds.

[0020] Yet another object of the present invention is to provide abullet trapping system that provides for simplified collection andremoval of spent rounds.

[0021] The present invention is a backstop for decelerating and trappingprojectiles. The backstop includes a support structure having an uppersurface and at least one “bin” region shielded from incoming rounds. Aprojectile trapping medium, preferably a mixture of a resilient granularballistic medium and a hydrated super absorbent polymer (SAP) gel, isdisposed on the upper surface and within the bins.

[0022] The bin regions are defined by one or more transverse baffles,such as angled stair-shaped segments or substantially vertical walls,spanning substantially the entire width of the backstop. Preferably, thebins are defined by one or more non-ricochet producing barriers.

[0023] Natural or induced vibrations will urge trapped rounds downwardsinto the bins, where they will be shielded from incoming fire. Inembodiments, the lower surface of one or more bins slopes downwardstoward either or both sides of the backstop, such that vibration willurge spent rounds towards collection points along the sides of thebackstop. Access ports may be provided in the backstop sidewallsproximate these collection points to allow for removal of spent rounds.The volume removed may be filtered (e.g., sieved) to reclaim projectiletrapping medium for reuse in the backstop.

[0024] Further advantages of the present invention will be apparent fromthe description below with reference to the accompanying drawings, inwhich like numbers indicate like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a side view of a bullet trapping backstop according to afirst embodiment of the present invention.

[0026]FIG. 2 is a side view of a bullet trapping backstop according to asecond embodiment of the present invention.

[0027]FIG. 3 is a side view of a bullet trapping backstop according to athird embodiment of the present invention.

[0028]FIG. 4 is cross-sectional view of the bullet trapping backstop ofFIG. 3, taken along line 4-4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0029] Referring now to the drawings, and specifically to FIGS. 1-3,there is shown a bullet trapping backstop 10 for decelerating andtrapping projectiles 12 traveling along a line of fire “a” towardsbackstop 10. (It should be understood that the terms “bullet,”“projectile,” and “round” are used interchangeably herein and refer toprojectiles or munitions of any sort or caliber.) Backstop 10 generallyincludes a foundation or support structure 14 having an upper surface 16and at least one bin 18. Bins 18 are regions shielded from the impact ofprojectiles 12 traveling along line of fire “a” (e.g., the regions belowthe dashed lines in FIGS. 1-3). One skilled in the art will understandthat support structure 14 may take any number of forms (e.g., a dirt orearth berm, a concrete pad, a steel frame, a wood frame) withoutdeparting from the scope of the present invention. Preferably, supportstructure 14 is formed of a non-ricochet producing material. Aprojectile trapping medium 20 is disposed (e.g., piled) on upper surface16 and within bins 18.

[0030] Projectile trapping medium 20 includes a resilient granularballistic medium, such as rubber chunks, wood chips, plastic scrap, orany other material that will not produce a ricochet when impacted by abullet. Rubber chunks are preferred because of their durability whensubjected to impacts from incoming bullets. Most preferably, projectiletrapping medium 20 is a mixture of a resilient granular ballisticmaterial and a hydrated super absorbent polymer (SAP) gel to form an“artificial soil” of ballistic material “chunks” in an SAP gel matrix.That is, the ballistic material serves as a framework to hold thehydrated SAP gel, and the hydrated SAP gel occupies interstices betweenparticles of ballistic material. This combination provides for a higherangle of repose α, a reduced likelihood of sluffing of projectiletrapping medium 20, and therefore the potential for a more compactbackstop 10 in the direction of line of fire “a.”

[0031] SAP will absorb up to 400 times its mass in water, such that theresulting hydrated SAP gel can be up to 97.5% water by mass, with nearlythe density of water. Thus, for bullet trapping backstops 10 maintainedoutside, rainfall enhances, rather than impairs, performance. SAPmaterial is marketed in a variety of forms (e.g., granules, powders, andfibers). Preferably, hydrated SAP gel is a sodium or potassium acrylate,acrylamide, or carboxylate polymer, or some combination thereof.Further, the mixture of ballistic material and SAP gel may be more than50% SAP by volume, such that there is a substantially reduced likelihoodof fire, thereby reducing or eliminating the need for flame retardantadditives.

[0032] Cross-linked polyacrylate and polyamide SAP gels are most stablewhen maintained in a wet condition with a pH above 4.5, as they tend toshrink and shed water in acids. Additionally, higher alkalinities reducethe solubility of lead and other heavy metal ions. Thus, in embodiments,at least one additive is mixed with hydrated SAP gel to maintain a pH ofat least 4.5, and preferably a pH between 8 and 12, inclusive. The mostpreferred additives, as discussed below, typically provide a pH ofapproximately 10.4.

[0033] Further, SAP gel has an inherent ability to bind lead. Forexample, Cetco, Inc. of Arlington Heights, Ill. claims that a granularcross-linked polyacrylate will absorb a 30 ppm lead solution, producinga volume change of 110 times the volume of the absorbent. Since most ofthe lead in backstop 10 will be in the form of metallic lead, however,it is also desirable to include at least one additive that will form apassive coating on the metallic particles, thereby preventing the leadfrom corroding, formulating soluble lead compounds, and leaching intothe environment.

[0034] The preferred additives generally have low solubility in water,and will typically remain as powdery solids in the mixture. Appropriatechoices are phosphates, carbonates, hydroxides, silicates, andbicarbonates, either singly or in combination. These additives can serveboth purposes discussed above. That is, they will both increase the pHof the SAP gel and prevent leaching of heavy metals into theenvironment. They can also help stabilize the hydrated SAP gelchemically, retard the growth of mold or bacteria in the hydrated SAPgel, and enhance the flame retardant characteristics of projectiletrapping medium 20. One skilled in the art will understand how to selectan appropriate cation, such as potassium, sodium, aluminum, magnesium,or calcium, for the additive. It will also be apparent to one skilled inthe art that different or additional additives may be used as well.However, as will be discussed below, the most preferred additives arecalcium phosphate, calcium carbonate, and aluminum hydroxide.

[0035] The use of buffering and passivating additives with SAP presentsadditional considerations. SAP absorbs less water per unit dry weightwhen the water around it contains large quantities of dissolvedmaterials. For example, a typical SAP will absorb approximately 50 timesits dry weight in water in a 1% NaCl solution, but only 22 times its dryweight in a 10% NaCl solution. Most buffering and passivating compoundsare most effective when they are in solution in reasonably constantconcentrations. Additionally, soluble forms of phosphorus can leach outof the SAP mixture, causing environmental pollution. Furthermore, anyphosphate precipitated as lead or copper phosphate is no longeravailable to act as a buffer.

[0036] The present invention preferably addresses these considerationsby using calcium phosphate compounds having low solubilities asadditives. The concentration of these calcium compounds in solution isnever high enough to alter the water absorbance of the SAP. However, asthe phosphate is removed by reactions with lead and copper, more solid(particulate) calcium phosphate dissolves to maintain a saturated, butnot very concentrated, solution. In addition to calcium phosphatecompounds, calcium carbonate and aluminum hydroxide are valuableadditives. Calcium carbonate provides additional buffering capacity,while aluminum hydroxide adds to the buffering capacity and can alsoreact with lead phosphates to form very insoluble lead aluminumphosphates.

[0037] It will be apparent to one skilled in the art how to produce anSAP mixture with a pH in the desired range and saturated with respect tothe additives used. One useful method of designing projectile trappingmedium 20 is to estimate the volume of ballistic material to be employedin backstop 10 and determine the proportion of interstices in thatvolume. Typically, this would be approximately 50% of the volume of theballistic material. Assume that the density of the hydrated SAP gelneeded to fill the interstices will approximate that of water andcalculate the weight of hydrated SAP gel required. Each additive canthen be added to projectile trapping medium as 5 to 10 parts of eachadditive for every 100 parts of hydrated SAP gel.

[0038] Bins 18 are created by constructing a series of transversebaffles 22 on upper surface 16. A non-ricochet producing material,preferably a shock absorbing, foamed, fiber-reinforced concrete such asSACON®, is used to construct baffles 22. Use of a non-ricochet materialensures that any projectiles 12 that are insufficiently decelerated byprojectile trapping medium 20 will partially or totally embed themselvesin baffles 22, where they will not interfere with the operation ofbackstop 10 or pose a hazard to personnel on the firing range. It shouldbe apparent to one skilled in the art that other non-ricochet producingmaterials, such as wood, plaster board, or rubber blocks, may also beused to construct baffles 22 without departing from the scope of theinvention, though foamed concrete is preferred for its safety anddurability. Projectiles 12 that are fully decelerated and trapped byprojectile trapping medium 20 will migrate, via gravity and natural orinduced vibration, into bins 18.

[0039] Bins 18 preferably have a minimum depth, measured along line offire “a,” at least three times greater than the largest dimension of theresilient granular ballistic material used in projectile trapping medium20. This ensures that projectile trapping medium 20 (specifically, theresilient granular ballistic material used therein) does not seal bins18 via bridging between baffles 22. Baffles 22, and therefore bins 18,preferably extend the full width of backstop 10, though narrower baffles22 are contemplated as within the scope of the invention. In addition tocreating bins 18, baffles 22 also serve to stabilize the sloping face ofprojectile trapping medium 20, thereby further reducing the likelihoodof sluffing and further increasing the angle of repose α to a valuelarger than about twenty-six degrees.

[0040]FIG. 1 shows a first embodiment of the backstop 10 according tothe present invention. In this embodiment, baffles 22 are formed as aseries of stair-shaped segments. The upper tread portions 24 of thesegments are sloped downwards away from the front of backstop 10 tocreate bins 18. A rear separator wall 26 is also provided, and a toeblock 28 may also be provided. One skilled in the art will recognizethat rear separator wall 26 ensures that no projectiles 12 travel beyondbackstop 10, except in cases of extreme aiming error, and that theheight of toe block 28 determines the height of the front-most bin 18.Similar to baffles 22, rear separator wall 26 and toe block 28 arepreferably constructed of a non-ricochet producing material.

[0041] A second embodiment of the backstop 10 is illustrated in FIG. 2.Baffles 22 are formed as one or more substantially vertical,substantially parallel walls disposed within projectile trapping medium20. Preferably, the walls are built to a height that approaches, butdoes not exceed, the overall top surface 30 of projectile trappingmedium 20.

[0042] As shown in FIGS. 3 and 4, which illustrate the most preferredembodiment of the present invention, the backstop 10 of FIG. 2 can bemodified to include an inclined plane base 32 in at least one bin 18.Bases 32 are inclined in at least one direction substantiallyperpendicular to the line of fire “a” and oriented to form at least onecollection point 34 proximate at least one sidewall 36 of backstop 10(e.g., higher nearer the centerline of backstop 10, sloping downwardstowards sidewall 36). Bases 32 may be integrally formed with supportstructure 14, but are preferably separately constructed within bins 18from an appropriate material. For example, a plurality of ramped blocksmay be disposed within one or more bins 18 to provide inclined bases 32.One or more ports 38, corresponding to the number of collection points34, are provided on sidewall 36 to facilitate access to collectionpoints 34, for example as a series of ramped blocks.

[0043] As noted above, some projectiles 12 will impact backstop 10 withsufficient velocity to embed themselves in baffles 22. Other projectiles12 will be fully decelerated by and trapped within projectile trappingmedium 20. The approximately eleven-fold difference in densities betweenprojectile trapping medium 20 and spent projectiles 12 will cause theseloosely trapped spent projectiles 12 to settle naturally towards thelowest point of backstop 10. As additional projectiles 12 impactbackstop 10, the resulting vibrations will further urge these spentprojectiles 12 downwards into bins 18, and, in embodiments, along bases32 towards collection points 34. If desired, vibrations may periodicallybe mechanically induced in backstop 10, for example with a vibrating rodor concrete (stinger-type) vibrator.

[0044] To maintain backstop 10, spent projectiles 12 are removed throughports 38, for example by using augers and scrappers. In contrast toprior art systems, spent projectiles 12 will be concentrated in the areaof ports 38 rather than randomly distributed throughout projectiletrapping medium 20 or concentrated in the impact area, which may not beeasily accessible via a trap door or other access port. Thus, thecleaning process will remove only a minimal volume of projectiletrapping medium 20. This combined volume removed may be filtered (forexample, sieved) to separate spent projectiles 12 from projectiletrapping medium 20, such that projectile trapping medium 20 may bereturned to backstop 10.

[0045] The resulting backstop reduces the leaching of heavy metals, thusprolonging the life of the trap. Trapped rounds are environmentallystabilized (by the chemical properties of either the hydrated SAP gel orbaffles 22) and isolated from incoming rounds, substantially reducingthe likelihood of ricochet, fragmentation, fire, environmental, andother hazards. This also substantially reduces the need to periodicallyclean the trap and reclaim spent rounds, while increasing the ease ofmaintenance when performed. Furthermore, the backstop is adapted for usewith various calibers and metals, and provides for a nearly noiselessbullet impact. The medium may also be used to quickly, simply, andsecurely anchor disposable papier-mache or cardboard targets, thusproviding a stable and transportable target display without the use ofitems that will produce a ricochet or require retrieval and removal.Such targets may be located at varying heights on a single trap bymounting them on baffles 22.

[0046] While the invention has been described in terms of its preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modifications within the spirit and scope of theappended claims. Thus, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings shall beinterpreted as illustrative rather than limiting, and the inventionshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A backstop for decelerating and trappingprojectiles traveling along a line of fire, said backstop comprising: asupport structure having an upper surface and at least one bin; and aprojectile trapping medium disposed on said upper surface and withinsaid at least one bin.
 2. The backstop according to claim 1, whereinsaid at least one bin is defined by at least one transverse baffleextending substantially a full width of said backstop.
 3. The backstopaccording to claim 2, wherein said at least one transverse bafflecomprises at least one angled stair-shaped segment.
 4. The backstopaccording to claim 2, wherein said at least one transverse bafflecomprises at least one substantially vertical wall disposed within saidprojectile trapping medium.
 5. The backstop according to claim 4,wherein said at least one substantially vertical wall is disposedentirely within said projectile trapping medium.
 6. The backstopaccording to claim 4, wherein said at least one substantially verticalwall is at least two substantially vertical, substantially parallelwalls.
 7. The backstop according to claim 2, wherein said at least onetransverse baffle comprises at least one non-ricochet producing barrier.8. The backstop according to claim 7, wherein said at least onenon-ricochet producing barrier comprises at least one shock absorbing,foamed, fiber-reinforced concrete barrier.
 9. The backstop according toclaim 8, wherein said shock-absorbing, foamed, fiber-reinforced concreteis SACON®.
 10. The backstop according to claim 1, wherein said at leastone bin further comprises a base inclined in at least one directionsubstantially perpendicular to the line of fire and oriented to form atleast one collection point proximate at least one sidewall of saidbackstop.
 11. The backstop according to claim 10, further comprising atleast one port on said at least one sidewall, said at least one portlocated to facilitate access to said at least one collection point. 12.The backstop according to claim 1, wherein said at least one bin extendsa full width of said backstop.
 13. The backstop according to claim 1,wherein said projectile trapping medium comprises a resilient granularballistic medium.
 14. The backstop according to claim 13, wherein adepth of said at least one bin, measured along the line of fire, is atleast three times greater than a largest dimension of particlescomprising said resilient granular ballistic medium.
 15. The backstopaccording to claim 13, wherein said projectile trapping medium furthercomprises a hydrated super absorbent polymer (SAP) gel mixed with saidballistic medium.
 16. A method of forming and maintaining a backstop fordecelerating and trapping projectiles traveling along a line of fire,comprising the steps of: providing a backstop comprising a supportstructure having an upper surface and at least one bin; and disposing aprojectile trapping medium on the upper surface and within the at leastone bin.
 17. The method according to claim 16, further comprising thestep of sloping a base of the at least one bin in at least one directionsubstantially perpendicular to the line of fire to form at least onecollection point proximate at least one side of the backstop.
 18. Themethod according to claim 17, further comprising the step of removingtrapped projectiles from the backstop at the at least one collectionpoint.
 19. The method according to claim 18, further comprising the stepof vibrating the backstop, thereby urging trapped projectiles towardsthe at least one collection point.
 20. The method according to claim 18,further comprising the steps of: filtering projectile trapping mediaincidentally removed from the backstop during said step of removingtrapped projectiles, thereby removing trapped projectiles; and returningthe filtered projectile trapping media to the backstop.